Re^3: Moose "unions" and inheritance

"Starting to grok the code, I 1st wondered why the type constraints do not need to be written in a string. It seems use MooseX::Types::Moose is responsible for being able to do that."

Moose type constraints are not strings, they are instances of Moose::Meta::TypeConstraint. has (and indeed the Moose::Meta::Attribute class that powers has) just gives you a little sugar allowing you to indicate type constraints as strings. But internally it translates those to type constraint objects.

MooseX::Types basically gives you functions defined along these lines:

# It's actually a lot more complex than this, but just
# pretend it's this simple...
#
sub HashRef () {   ### empty prototype
  return Moose::Meta::TypeConstraint->lookup('HashRef');
}
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So that you can use:

    isa => HashRef
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It also plays some fancy tricks overloading bitwise operators so that HashRef | ArrayRef "just works".

So everything I did in the previous example would work without MooseX::Types; you'd just need to do a bit of work with Moose::Meta::TypeConstraint objects, so it wouldn't look as pretty.

"Indicating, that only the 1st one in the inheritance hierarchy gets propagated. So I assume for it to work independent of how many parent classes were passed, one would have to loop over them in _existing_constraint (how?) and buildup the type constraint before returning it."

Multiple inheritance is always going to make things messier. For example, if you're inheriting from classes A and B where:

package A;
has data => (is => 'ro');
package B;
has data => (is => 'rw');
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... what on earth would you expect to happen?!

In cases like this, I'd want the class that's doing the multi-inheritance to define as much of the data attribute as it can, and rely on its base classes' definitions as little as possible.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

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Re^4: Moose "unions" and inheritance
by PetaMem (Priest) on Nov 30, 2012 at 13:49 UTC

Moose type constraints are not strings, they are instances of Moose::Meta::TypeConstraint.

Moose::Manual::Types

...
isa => Str | ArrayRef,
...
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doesn't work without MooseX::Types (Bareword "Str" not allowed while "strict subs"...)

package ValAtom;

use strict;
use warnings;
use 5.10.1;

use Moose;
use MooseX::Types::Moose -all;

extends 'KeyAtom', 'JustTesting';

has '+data' => (
    isa     => __PACKAGE__->_existing_constraint('data') . ' | ArrayRe
+f | HashRef',
);

sub _existing_constraint {
        my ($class, $attr) = @_;
        return join ' | ', map {
            $_->meta->find_attribute_by_name($attr)->type_constraint
        } $class->meta->superclasses;
    }

1;
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Bye
PetaMem All Perl: MT, NLP, NLU

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